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Testing & modern typing

pytest basics, mocks, type hints, TypedDict, Protocol, and static-checking patterns.

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Generate Fake User Data with Faker in Python

Use the Faker library to generate realistic fake user profiles with names, emails, phone numbers, and addresses for tests or demos.

faker fake-data testing

Python

from faker import Faker

fake = Faker()

def generate_user():
    return {
        "name": fake.name(),
        "email": fake.email(),
        "phone": fake.phone_number(),
        "address": fake.address().replace("\n", ", "),
    }

if __name__ == "__main__":
    user = generate_user()
    for key, value in user.ite…

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Testing & modern typing easy

How to Compare Files and Show a Diff in Python

Compare two text files and print a unified diff using Python's difflib module to highlight differences.

diff files difflib

Python

import difflib
from pathlib import Path

def compare_files(expected_path: str, actual_path: str) -> str:
    """Compare two text files and return a unified diff."""
    expected = Path(expected_path).read_text()
    actual = Path(actual_path).read_text()

    diff = difflib.unified_diff(
        expected.splitlines(ke…

10 0 Open

Testing & modern typing easy

How to Mock open() in Python for Reading File Data

This example shows how to mock Python's built-in open() function using unittest.mock to simulate file reading without touching the disk.

mock unittest file-io

Python

import builtins
from unittest.mock import patch

def read_file_data(filename):
    with open(filename, 'r') as f:
        return f.read()

def mock_read_data():
    fake_data = "This is mocked file content"
    
    class FakeFile:
        def __enter__(self):
            return self
        def __exit__(self, *args):…

14 0 Open

Testing & modern typing easy

How to Mock pathlib Path.read_text with mock_open in Python

Mock pathlib.Path.read_text using patch and mock_open to test file-reading code without touching the filesystem.

testing mock pathlib

Python

import pathlib
from unittest.mock import mock_open, patch

def read_config(filepath: pathlib.Path) -> str:
    """Read file content with pathlib."""
    return filepath.read_text()

if __name__ == "__main__":
    mock_data = "version: 1.0\nname: demo-app"
    
    with patch("pathlib.Path.open", mock_open(read_data=mo…

14 0 Open

Testing & modern typing easy

How to Use the pytest tmp_path Fixture for Temporary Directories

Use pytest's built-in tmp_path fixture to create a unique temporary directory per test for clean file I/O testing.

pytest tmp_path fixtures

Python

import pytest


def test_write_and_read_file(tmp_path):
    # tmp_path is a pytest fixture that provides a temporary directory
    # unique to each test invocation
    data_file = tmp_path / "data.txt"
    data_file.write_text("hello world")
    assert data_file.read_text() == "hello world"


def test_multiple_tmp_pat…

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